Vibration is a destructive force in a variety of environments. For example, a vehicle experiencing vibration from traveling over a road can damage the structure of the vehicle. Vibration between a vehicle frame and the vehicle cabin can tire a driver. Vibration from an earthquake can topple a structure, such as a building, elevated highway or bridge. Vibration from a air conditioning unit mounted on top of a building can create fatigue and failure of welds within the unit. Vibration at resonant frequency will build upon itself and destroy the unit.
Vibration can be periodic, as created by a rotating compressor in an air conditioning unit or an engine in a car. Periodic vibration is characterized by a particular frequency and amplitude. Random vibration, on the other hand, has no dominant frequency and no dominant amplitude. Instead, the vibration must be analyzed quantitatively to determine average amplitudes and common frequencies. Damping is the process by which vibration steadily diminishes in amplitude. In damping, the energy of the vibrating system is dissipated as friction or heat, or transmitted as sound. The process of damping can take any of several forms, and often more than one form is present.
A liquid spring utilizes a compressible fluid to provide damping forces. A liquid spring can comprise a cylindrical housing having an internal chamber with a compressible liquid therein, a piston reciprocally disposed in the chamber, and a rod structure axially movable into and out of the chamber, secured to the piston, and having an outer longitudinal portion projecting outwardly of one of the housing ends. If a liquid spring is used between a vehicle frame and an associated wheel support structure, the compressible liquid within the liquid spring generates both spring and damping forces in the suspension system in response to relative axial translation between the rod structure and housing of the liquid spring caused by relative vertical displacement between the wheel and the frame. A more detailed description of the general structure and operation of a liquid spring incorporated in a vehicular suspension system may be found in U.S. Pat. No. 4,741,516 entitled "Fluid Suspension Spring and Damper for Vehicle Suspension System" and U.S. Pat. No. 5,316,272 entitled "Liquid Spring Vehicular Suspension System and Associated Control Apparatus," which are incorporated herein by reference.
A need exists for the benefits of a liquid spring in a variety of environments. For example, a need exists for a method of protecting a structure, such as a building, from the destructive vibration from an earthquake. A need also exists for a method of minimizing the vibration transmission between a vehicle's frame and the vehicle's cabin. A need exists for a method of controlling vibration between a stable platform and a piece of machinery which vibrates, such as a motor, fan, compressor, pump, or engine.